ld-wasm linker problem in corert

gistfile1.txt

I'm trying to build the wasm target using llvm9 and I'm getting this error on linking

Microsoft (R) Program Maintenance Utility Version 14.20.27508.1
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[  1%] Linking CXX static library libPortableRuntime.bc
wasm-ld: error: symbol type mismatch: RhpInterfaceDispatch1
>>> defined as WASM_SYMBOL_TYPE_DATA in CMakeFiles/PortableRuntime.dir/__/CachedInterfaceDispatch.cpp.o
>>> defined as WASM_SYMBOL_TYPE_FUNCTION in CMakeFiles/PortableRuntime.dir/__/portable.cpp.o

wasm-ld: error: symbol type mismatch: RhpInterfaceDispatch2
>>> defined as WASM_SYMBOL_TYPE_DATA in CMakeFiles/PortableRuntime.dir/__/CachedInterfaceDispatch.cpp.o
>>> defined as WASM_SYMBOL_TYPE_FUNCTION in CMakeFiles/PortableRuntime.dir/__/portable.cpp.o

If I run llvm-dumpobj on the 2 files in question you can see the mismatch, CachedInterfaceDispatch.cpp.o:

00000000 g     O *UND* RhpInterfaceDispatch1
00000000 g     O *UND* RhpInterfaceDispatch2

and portable.cpp.o:

00000ec5 g     F CODE .hidden RhpInterfaceDispatch1
00000f13 g     F CODE .hidden RhpInterfaceDispatch2

I had a short conversation on the llvm IRC chat where they seemed to confirm that the compilation and linker were correct 
and the code could be modified:

<yowl00> extern "C" void (*RhpInterfaceDispatch2)(); <- would you expect clang to output as an undefined data symbol or undefined function symbol?
* V|r (~Vir@p508797D4.dip0.t-ipconnect.de) has joined
<yowl00> it makes it an undefined data symbol which sounds right, its just a pointer, no?
<compnerd> yowl00: undefined data symbol
<yowl00> compnerd: that's good, no problem with the object file generation then.  And the linker should be able handle marrying that up to the actual definition which would be a function symbol?
<compnerd> yowl00: nope
<compnerd> yowl00: that will give you an undefined symbol after you link
<compnerd> you need do an explicit `extern "C" void (*RhpInterfaceDispatch2)() = &RhpInterfaceDispatch2Implementation;`
<yowl00> compnerd: I get a symbol type mismatch, so there's some glue missing
<compnerd> the `&` is obviously optional - the type conversion should kick in on that
<compnerd> yowl00: nope, no glue mismatch, you cannot just define a function `RhpInterfaceDispatch2`
<compnerd> that is supposed to be a pointer to the implementation, note the fact that assignment has a suffix
<compnerd> you could do an `extern "C" void RhpInterfaceDispatch2()` if you don't want the indirection
<yowl00> compnerd: what about an extern with a body like https://github.com/dotnet/corert/blob/master/src/Native/Runtime/portable.cpp#L219
<yowl00> where that macro is EXTERN_C REDHAWK_API _rettype __fastcall _method _args
<compnerd> an `extern` with a body or an `extern "C"` with a body?
<yowl00> extern "C"
<compnerd> yeah, that wont work
<compnerd> that will define the the function with the same name
<yowl00> ok, I need to do some more reading, this code compiles somehow, I'm just trying it with llvm/clang9/ld-wasm
<compnerd> it will compile, but fail to link
<yowl00> yes, that's my problem wasm-ld doesn't like the symbol mismatch.  Maybe I should see what it does when I build for x64 rather than wasm
<compnerd> yowl00: where is the pointer to it in the code?
<compnerd> yowl00: although! that is .NET core ... they could be doing that across a module boundary and it will work just fine on Windows
compnerd> they could be manually handling the `__declspec(dllimport)` in that case
<yowl00> compnerd: these pointers are stored in an array https://github.com/dotnet/corert/blob/d725e5cbdfe58d70b193affc16519ccc367597fe/src/Native/Runtime/CachedInterfaceDispatch.cpp#L233-L241
<compnerd> yowl00: lol, I see ... yes, that will work unless your linker is clever enough to realize that they type is different; just make those function declarations instead


So is it going to be ok to change the externs in CachedInterfaceDispatch to functions rather than function pointers?

You can see the changes I made to get past this https://github.com/dotnet/corert/compare/master...yowl:llvm8?expand=1#diff-782c2940871512b170b7f2f49c0ddf6d and https://github.com/dotnet/corert/compare/master...yowl:llvm8?expand=1#diff-7437be93850382bb0c06e8f2068addb8